B1G REVISION NOTES

Gene control

Every cell in our body contains a nucleus ( except red
blood
cells ) which contains the genetic information, unique to
that individual

Each human being has 23 pairs of chromosomes ( equals
46 ) in each nucleus in the body

Number of
chromosomes
in
Eggs Sperm cells or pollen Body
cells cells cells
Hawkweed 4 4 8

Sedge 21 21 42

Hen 18 18 36

Human 23 23 46

Kangaroo 6 6…

DNA

DNA ( stands for deoxy rilo nucleic acid ) has a twisted
double ­ heux structure like a twisted ladder
Each ` rung ' on the ladder is made of a pair of basis
There are 4 types of basis G, C, A and T
G and C always…

Sections of DNA are called genes
We inherit half our genes from our father and half our
genes from our mother
Sex cells are the only cells to contain only half the
chromosomes




Gender




Males are said to be XY and females XX ­ mostly because
of the shape of…

The egg contains twenty ­ two ` body ' chromosomes and
one sex chromosome
It can only be an X chromosome so all eggs have an X
From the father ( XY )
Sperm also have twenty ­ two ` body ' chromosomes
Half the sperm have an X chromosome…